This invention relates in general to the chemical treatment of a workpiece where it is desired to chemically treat only one side of the workpiece and eliminate the need to process the othre side with a protective coating.
This invention relates, in particular, to chemically treating, as by etching or anodizing, a semiconductor wafer on one side only by a method and apparatus in which the one side of the wafer can be so treated without the need of providing a protective coating on the other side so that the latter side will not react to the chemical treatment as in the case of the presently known methods.
There are many instances when it is desired to perform work on only one side of the workpiece, as for example, in semiconductor processing where it is often only necessary to etch or anodize only one surface of a semiconductor wafer without disturbing the other surface. Whether the process was etching or anodizing the one surface, it has heretofore been necessary to coat the opposite surface with a protective layer to prevent that surface from reacting with the liquid chemical, and in the case of anodization, to immerse most of the wafer into the solution with a positive potential applied to the edge of the wafer, via a clip, and a negative potential applied to the liquid. In this process not all the surface to be anodized was utilized since the clip edge of the wafer must remain out of the solution. Thus, the step of adding the protective coating on the side not to be treated and the loss of the portion of the full wafer were extra costs that increased the ultimate cost of the manufacture of the end product.
Another known prior art method of processing a workpiece, such as a semiconductor wafer where only one side of the wafer is to be chemically treated, is to attach vacuum cups or other attaching means to the other side of the wafer and suspend the side to be treated into the solution to a depth less than the thickness of the wafer. This method is also expensive because of the cost of the attaching means and the difficulties involved in precisely suspending the wafer into the solution so as not to affect the top side of the wafer. The only way to protect the top of the wafer in this method, of course would be to add a protective coating to the top side where the vacuum cups are attached but this also is an additional cost even though this process would eliminate the loss of the area of the wafer where the clip leads were attached in the process described above.
Another method is to attach the waferback to a suction cup covering the entire back surface and making electrical contact within the cup. The fixture is then submerged and only one side is exposed. However, maintaining a perfect seal to the wafer edge under vacuum has proven very troublesome.